Wood-type golf club head

ABSTRACT

A wood-type golf club head comprises a hollow structure having a geometrical arrangement for improving the directionality and carry distance of the struck ball, wherein the ratio (W/L) of a size (W) of the head in the back-and-forth direction to a size (L) of the head in the toe-heel direction is 0.85 to 1.0; and the ratio (FP/GL) of a face progression (FP) of the head to a depth (GL) of the center of gravity of the head is 0.50 to 0.75.

BACKGROUND OF THE INVENTION

The present invention relates to a wood-type golf club head, more particularly to a geometrical arrangement for improving the directionality and carry distance of the struck ball.

In the case of a wood-type golf club head having a large lateral moment of inertia, even if the ball hitting position is off the sweet spot towards the toe or heel, the rotation of the club head at impact around a vertical axis passing the center of gravity becomes small and as a result, directionality of the struck balls is stabilized.

The lateral moment of inertia of a golf club head can be increased by increasing the head size as the trend of the wood-type golf club heads.

On the other hand, in a club head (a) being large in the size in the back-and-forth direction, as shown in FIG. 7, the distance (A) backward from the club shaft axis CL to the center of gravity G of the head becomes increased. Accordingly, during swing, due to the centrifugal force, the club head (a) is subjected to a rotation moment MO which causes a rotation such that the center of gravity G of the head approaches the club shaft axis CL as shown in imaginary line (clockwise rotation when viewed from the heel-side as shown in FIG. 7), and as a result, the dynamic loft angle of the club face (b) at impact becomes larger than the specified loft angle (real loft angle). In the case of the club head subjected to such a large rotation moment MO during swing, missed shots with the leading edge Le so called topped shots are very liable to occur.

Also, the ball hitting position tends to shift towards the sole, therefore, the backspin of the ball is increased due to the vertical gear effect.

Thus, there is a tendency that the trajectory of the ball becomes so called “ballooning” or “rising” trajectory and thereby the carry distance is decreased.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a wood-type golf club head, in which the above-mentioned rotation moment during swing can be decreased to improve the directionality and carry distance of the struck ball.

According to the present invention, a wood-type golf club head comprises a hollow structure wherein

the ratio (w/L) of a size W in the back-and-forth direction of the head to a size L in the toe-heel direction of the head is 0.85 to 1.0, and

the ratio (FP/GL) of a face progression FP of the head to a depth GL of the center of gravity of the head is 0.50 to 0.75.

Definitions:

In this specification, dimensions, positions, directions and the like relating to the club head refer to those under a standard state of the club head unless otherwise noted.

Here, the standard state of the club head is such that the club head is set on a horizontal plane HP so that the axis CL of the club shaft is inclined at the lie angle (beta) while keeping the axis CL on a vertical plane VP, and the club face 2 forms its loft angle (alpha) with respect to the horizontal plane HP. Incidentally, in the case of the club head alone, the center line of the clubshaft inserting hole of the hosel can be used instead of the axis CL of the clubshaft.

“Sweet spot SS” is the point of intersection between the club face 2 and a straight line N drawn normally to the club face 2 passing through the center of gravity G of the head.

“Back-and-forth direction” is a direction parallel with the straight line N projected on the horizontal plane HP.

“Heel-and-toe direction” is a direction parallel with the horizontal plane HP and perpendicular to the back-and-forth direction.

“Up-and-down direction” is a direction perpendicular to the horizontal plane HP.

“Lateral moment of inertia” is the moment of inertia of the head around a vertical axis passing through the center of gravity G.

“Face progression FP” is the horizontal distance of the leading edge Le of the club head 1 from the vertical plane VP including the club shaft center line CL, measured in a vertical plane VP1 including the sweet spot SS and the center of gravity G.

“Depth GL of the center of gravity G” is the horizontal distance between the leading edge Le and the center of gravity G measured in the vertical plane VP1.

“Leading edge Le” is a contact point between the club face 2 and a vertical plane P4 parallel with the vertical plane VP, occurring on the vertical plane VP1.

“Size L of the club head in the toe-heel direction” is the distance between the club shaft axis CL and a toe-side farthest point T. The toe-side farthest point T is a point on the outer surface of the head which is farthest from the club shaft axis CL when viewed from the front of the head as shown in FIG. 2. The distance is measured in a direction perpendicular to the club shaft axis CL and parallel to the vertical plane VP.

“Size W of the head in the back-and-forth direction” is the distance between a plane P3 tangent to the sweet spot SS and a back-side farthest point B. The farthest from the plane P3 is a point on the outer surface of the head which is farthest from the plane P3 when viewed from the toe or heel side of the head as shown in FIG. 4. The distance is measured in a direction perpendicular to the plane P3 and parallel to the vertical plane VP1.

“Gravity distance GSL” is a length of a straight line X drawn from the center of gravity G to the club shaft axis CL perpendicularly to the club shaft axis CL.

“Wood-type golf club” is meant for at least number 1 to 5 woods, and clubs comprising heads having similar shapes may be included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a wood-type golf club head according to the present invention.

FIG. 2 is a front view thereof.

FIG. 3 is a top view thereof.

FIG. 4 is a cross sectional view taken along line A-A in FIG. 3.

FIG. 5 is a heel-side view thereof.

FIG. 6 is a schematic heel-side view of a club head for explaining the effect of the present invention which reduces the rotation moment mo during swing.

FIG. 7 is a schematic heel-side view of a club head for explaining the problems caused by a large rotation moment MO during swing.

FIG. 8 is a graph showing the ranges defined by the limitations of the ratios (W/L) and (FP/GL).

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In the drawings, wood-type golf club head 1 according to the present invention comprises: a face portion 3 whose front face defines a club face 2 for striking a ball; a crown portion 4 intersecting the club face 2 at the upper edge 2 a thereof; a sole portion 5 intersecting the club face 2 at the lower edge 2 b thereof; a side portion 6 between the crown portion 4 and sole portion 5 which extends from a toe-side edge 2 c to a heel-side edge 2 d of the club face 2 through a back face BF of the club head; and a hosel portion 7 at the heel side end of the crown to be attached to an end of a club shaft inserted into the shaft inserting hole 7 a. Thus,.the club head 1 is provided with a hollow (i) and a shell structure with the thin wall.

In order to reduce the weight of the head, nonmetal materials, for example, ionomer resins, fiber reinforced resins and the like can be used to form a part of the club head 1. But, in this example, the club head 1 is made of one or more metal materials only. Various metal materials, for example, stainless alloys, maraging steels, pure titanium, titanium alloys, magnesium alloys, aluminum alloys and the like can be used.

The club head 1 can be manufactured by assembling two or more (usually up to 5 or 6) parts each prepared through a suitable process for example, casting, forging, pressure molding or the like.

In this embodiment, the head is for a number 1 wood.

The volume of the club head 1 is preferably not less than 400 cc, more preferably not less than 420 cc, still more preferably not less than 430 cc in order to increase the moment of inertia and the depth of the center of gravity to improve the directionality and also to make it easy to address the ball. However, to prevent an excessive increase in the club head weight and deteriorations of swing balance and durability, and also to comply golf rules, the club head volume is preferably not more than 470 cc, more preferably not more than 460 cc.

The mass of the club head 1 is preferably not less than 180 grams, more preferably not less than 183 grams, still more preferably not less than 185 grams in view of the swing balance, rebound performance and easiness of swing, but preferably not more than 220 grams, more preferably not more than 215 grams, still more preferably not more than 213 grams.

The lateral moment of inertia of the club head 1 is preferably not less than 4000 g sq.cm, more preferably not less than 4100 g sq.cm, still more preferably not less than 4200 g sq.cm. Therefore, even if the ball hitting position is off the sweet spot toward the toe or heel, the rotation of the head at impact around the vertical axis passing through the center of gravity G can be reduced. As a result, the deterioration of directionality can be avoided. However, if the lateral moment of inertia is too large, then there is possibility that the club head weight unavoidably increases or the shape of the club head becomes peculiar. Therefore, the lateral moment of inertia is preferably not more than 5900 g sq.cm, more preferably not more than 5800 g sq.cm.

If the depth GL of the center of gravity G is too small, then the lateral moment of inertia is liable to becomes insufficient, deteriorating the directionality, and as a result, the carry distance tends to decrease. Therefore, the depth GL is preferably not less than 30 mm, more preferably not less than 32 mm, still more preferably not less than 33 mm. But, if the depth GL is too large, on the other hand, the impact feeling is liable to become not good. Therefore, the depth GL is preferably not more than 60 mm, more preferably not more than 57 mm, still more preferably not more than 55 mm.

If the face progression FP is too small, then there is a tendency that the timing of hitting the ball is delayed and the club face 2 is closed at impact, therefore, the ballistic height tends to become lower and the distance is decreased. In this light, the face progression FP is preferably not less than 15 mm, more preferably not less than 16 mm, still more preferably not less than 17 mm. But, if the face progression FP is too large, on the other hand, then there is a tendency that the timing of hitting the ball becomes early and the club face 2 is opened at impact to hit a slice. In this light, the face progression FP is preferably not more than 35 mm, more preferably not more than 34 mm, still more preferably not more than 32 mm.

If the size W of the club head in the back-and-forth direction is too small, then the moment of inertia and the depth GL of the center of gravity G are decreased and the directional stability of the struck ball is liable to deteriorate. Further, the largeness of the head that the user feels is lessened and as a result the easiness of addressing the ball is also lessened. In this light, the size W in the back-and-forth direction is preferably not less than 100 mm, more preferably not less than 105 mm, still more preferably not less than 110 mm. If on the other hand, the size W is too large, then the height of the sweet spot SS is increased. As a result, the backspin is increased, and the trajectory is liable to become a rising trajectory and thereby the carry distance is again decreased. In this light, the size W in the back-and-forth direction is preferably not more than 127 mm.

If the size L of the club head 1 in the toe-heel direction is too small, then it becomes difficult to hit the ball at the sweet spot, and further the gravity distance GSL is decreased, which increase the tendency to hit a hook. In this light, the size L in the toe-heel direction is preferably not less than 105 mm, more preferably not less than 110 mm, still more preferably not less than 115 mm. If the size L is too large, on the other hand, there is a possibility of deterioration in holding the ball, therefore, the size L is preferably not more than 127 mm.

In order that the face portion 3 is provide with a sufficient strength against mechanical shocks at the time of hitting balls, the thickness of the face portion 3 is larger than those of the crown portion 4, sole portion 5 and side portion 8. As a result, the face portion 3 has a weight of about 30 to 40% of the gross weight of the club head.

On the other hand, it is effectual for increasing the lateral moment of inertia to increase the distance of the center of gravity G of the head from the face portion 3. Therefore, the ratio (W/L) of the size W (mm) to the size L mm) is set to be not less than 0.85, preferably not less than 0.86, more preferably not less than 0.88, still more preferably not less than 0.92. Namely, the size W is increased in relation to the size L to increase the moment of inertia and the depth GL of the center of gravity G, thereby even if the ball hitting position is off the sweet spot towards the toe or heel, the rotation of the club head at impact is reduced to improve the directionality. Further, since the size L can be appropriately controlled, slice can be prevented.

However, if the ratio (W/L) is too large, it becomes difficult for the user to rotate the head during swing to the proper address position, and as a result, the holding of the ball by the face becomes worse, and in the case of beginners in particular, there is a possibility of hitting a slice and thereby decreasing the carry distance. In this light, the ratio (W/L) is preferably not more than 1.0, more preferably not more than 0.99, still more preferably not more than 0.96.

Further, the ratio (FP/GL) of the face progression FP to the above-mentioned depth GL is set to be not less than 0.50, preferably not less than 0.54, more preferably not less than 0.61, still more preferably not less than 0.65.

By increasing the ratio (FP/GL) as above, as the distance A(=GL-FP) from the vertical plane VP to the center of gravity G is decreased and the above-mentioned rotation moment is decreased. Accordingly, the rotational motion of the center of gravity G towards the shaft axis CL caused by the centrifugal force during swing is controlled. As a result, possibility of missed shots such as topped shot and shot on the sole-side can be decreased. Further, an excessive increase of the dynamic loft angle can be prevented. Accordingly, an excessive increase of the launch angle of the struck ball is also prevented. Thus, the missed shots and so called “rising” trajectory can be prevented to improve the directionality and carry distance.

If the ratio (FP/GL) is less than 0.50, it becomes difficult to control the above-mentioned rotational motion sufficiently, therefore, the above-mentioned advantageous effects can not be obtained. However, if the ratio (FP/GL) is too large, there is a possibility that the face progression FP is unfavorably increased and/or the depth GL is unfavorably decreased. Therefore, the ratio (FP/GL) is preferably not more than 0.75, more preferably not more than 0.72, still more preferably not more than 0.70.

As explained above, with the increase in the ratio (W/L), the moment of inertia and the depth of the center of gravity are advantageously increased. But, there is a tendency that the above-mentioned rotational motion during swing is increased to decrease the carry distance. Therefore, it is desirable that the ratio (FP/GL) is increased with the ratio (W/L) is increased. The inventor discovered that the carry distance and directionality can be improved in a well-balanced manner by satisfying the following conditional expression (1), preferably (2).

(FP/GL)−0.6X(W/L)>=0   (1)

(FP/GL)−0.6X(W/L)>=0.03   (2)

If the value of (FP/GL)−0.6X(W/L) becomes excessively large, however, it is unavoidable that the ratio (W/L) becomes unfavorably decreased, or that the ratio (FP/GL) becomes unfavorably increased. Therefore, it is preferable that the following conditional expression (3) is also satisfied.

(FP/GL)−0.6X(W/L)=<0.19   (3)

Furthermore, if it is considered that the increase in the carry distance is important more than the improvement in the directionality, it is preferable that the following conditional expression (4) is satisfied.

(FP/GL)−0.6X(W/L)>=0.11   (4)

Contrary, if it is considered that the improvement in the directionality is important more than the increase in the carry distance, it is preferable that the following conditional expression (5) is satisfied.

(FP/GL)−0.6X(W/L)=<0.11   (5)

FIG. 8 is a graph showing the numerical ranges limited or defined as above.

Comparative Tests

Wood-type golf club heads having the basic structure shown in FIGS. 1 to 4 and specifications shown in Table 1 were prepared and tested for the carry distance and directionality.

Each of the club heads was composed of an open-front hollow structure (m) and a face plate (f) laser-welding thereto so as to cover the front opening as shown in FIG. 1, wherein the weld line is indicated in broken line. The hollow structure (m) was formed by casting a titanium alloy Ti-6Al-4V. The face plate (f) was made of a high modulus alpha+bata titanium alloy (“SP700HM” manufactured by JFE steel corporation.) comprising 4.0 to 5.0 wt % Al, 2.5 to 3.5 wt % V, 1.8 to 2.2 wt % Mo, 1.7 to 2.3 wt % Fe, the balance being essentially Ti and incidental impurities. The face plate (f) was formed by means of press molding and NC machining to have a central thick portion and a peripheral thin portion. The center of gravity and the lateral moment of inertia were adjusted by changing the thickness of the sole portion and side portion.

Specifications common to all of the club heads are as follows:

Mass of head: 200 grams

Head volume: 460 cc

Loft angle: 11 degrees

Thickness of crown portion: 0.7 mm

Thickness of face portion

-   -   Thick central portion: 3.2 mm     -   Thin peripheral portion: 2.2 mm

In the tests, the club heads were attached to identical shafts to make 45-inch #1 wood clubs. Then, with respect to each of the heads, ten right-handed golfers having handicap ranging from 15 to 30 hit golf balls ten times per each, and the carry distance was measured to obtain the average carry distance.

Also, the difference of the ball landing position from the target trajectory was measured to obtain its absolute value regardless of whether the trajectory is rightward or leftward, and the mean value of the absolute values was computed.

At the same time, the directionality was evaluated by the ten golfers into five ranks (5: very good, 4: good, 3: average, 2: not good, 1: bad). The mean value of the rank numbers of the ten golfers was computed.

Furthermore, each head was evaluated by the ten golfers whether it is easy to rise the ball or not, and ranked into five as follows (5: very good, 4: good, 3: average, 2: not good, 1: bad). The mean value of the rank numbers of the ten golfers was computed.

These results are shown in Table 1.

From the test results, it was confirmed that the carry distance can be increased while improving the directionality.

As described above, in the wood-type golf club head according to the present invention, as the ratio (W/L) is limited between 0.85 and 1.0, a sufficient large lateral moment of inertia can be secured, while maintaining the center of gravity being deep. Accordingly, even if the ball hitting position is off the sweet spot towards the toe or heel, the rotation of the club head at impact is decreased, and the directionality can be stabilized. Further, as the ratio (FP/GL) is limited between 0.50 and 0.75, the above-mentioned rotation moment caused by the centrifugal force during swing is controlled. Therefore, unfavorable topped shots and rising trajectory are prevented and the carry distance can be improved. Thus, the directionality and carry distance are improved.

TABLE 1 Head Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Lateral moment of inertia (g sq. cm) 4950 5000 5100 4750 4800 4800 4850 Back-and-forth size W (mm) 115 117 117 108 108 108 112 Toe-heel size L (mm) 120 118 118 126 126 126 122 Face progression FP (mm) 23 21 28 18 26 23 22 Depth GL of center of gravity (mm) 38 38 40 36 37 37 38 FP/GL 0.61 0.55 0.70 0.50 0.70 0.62 0.58 W/L 0.96 0.99 0.99 0.86 0.86 0.86 0.92 (FP/GL)-0.6X(W/L) 0.03 −0.04 0.11 −0.01 0.19 0.11 0.03 Test results Carry (yard) 225 218 227 220 229 226 224 Difference (yard) 12 14 14 14 14 15 11 Directionality 3.8 3.7 3.6 3.6 3.5 3.6 3.9 Easiness of rising 4.2 3.7 4.5 4.0 4.6 4.4 4.4 Head Ex. 8 Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ex. 9 Lateral moment of inertia (g sq. cm) 4900 4600 4900 5000 5000 4750 Back-and-forth size W (mm) 112 101 117 117 120 108 Toe-heel size L (mm) 122 127 118 118 115 126 Face progression FP (mm) 19 25 28 17 23 19 Depth GL of center of gravity (mm) 38 35 36 38 40 35 FP/GL 0.50 0.71 0.78 0.45 0.58 0.54 W/L 0.92 0.80 0.99 0.99 1.04 0.86 (FP/GL)-0.6X(W/L) −0.05 0.24 0.18 −0.15 −0.05 0.03 Test results Carry (yard) 219 227 226 215 217 224 Difference (yard) 10 22 17 13 18 13 Directionality 3.9 3 3.2 3.8 3.2 3.7 Easiness of rising 3.9 4.6 4.4 3.5 3.8 4.1 

1. A wood-type golf club head comprising a hollow structure wherein the ratio (W/L) of a size (W) of the head in the back-and-forth direction to a size (L) of the head in the toe-heel direction is 0.85 to 1.0, and the ratio (FP/GL) of a face progression (FP) of the head to a depth (GL) of the center of gravity of the head is 0.50 to 0.75.
 2. The golf club head according to claim 1, which has a head volume of from 400 to 470 cc.
 3. The golf club head according to claim 1, which has a lateral moment of inertia of from 4000 to 5900 g sq.cm.
 4. The golf club head according to claim 2, which has a lateral moment of inertia of from 4000 to 5900 g sq.cm.
 5. The golf club head according to claim 1, wherein the ratio (FP/GL) is 0.65 to 0.75.
 6. The golf club head according to claim 1, wherein 0=<(FP/GL)−0.6X(W/L)=<0.19. 